Fixed the missing header file problem when compiling under Linux

[jimwang118]

When I compile microsoft-signalr[core,messagepack] under Linux, the following problem occurs.

/mnt/vcpkg/buildtrees/microsoft-signalr/src/1.0-alpha4-e34fa42a98/src/signalrclient/binary_message_parser.h:13:62: error: ‘size_t’ has not been declared
/mnt/vcpkg/buildtrees/microsoft-signalr/src/1.0-alpha4-e34fa42a98/src/signalrclient/transport_factory.cpp:26:20: error: ‘runtime_error’ is not a member of ‘std’
Line 39:    26 |         throw std::runtime_error("not implemented");

Solve the above problem by adding the missing header file.

[jimwang118]

@dotnet-policy-service agree company="Microsoft"

[sweemer]

Hello, can this be merged? I'm still getting this compiler error with the latest main branch on Linux.